An electronic component, e.g., a quartz oscillator, is housed within a package which includes a housing made of such as a ceramic and a lid for sealing an opening of the housing, for example, in a hermetic state so that a sealed electronic component is constituted.
While, as a sealing method of the sealed electronic component, the seam welding has been applied conventionally, the method includes the steps of brazing an expensive Kovar ring via a silver brazing material on the opening of the housing and of seam-welding the lid thereon, requiring a number of processes and high cost. In addition, it has been difficult to miniaturize the sealed electronic component substantially. Moreover, while there is a vacuum furnace welder to weld the lid to the housing by heating the housing in vacuum and fusing a sealing material, which is excellent in terms of the cost and productivity, it welds the sealing material over the entire circumference at one time, so that outgas from the sealing material produced upon welding is confined in the interior of the package, causing a problem of reduction in a degree of vacuum. As a result, sealing by the electron beam welding is performed instead of such as the seam welding.
FIG. 28 is a plan view for describing the method of the electron beam welding, which illustrates a locus of an electron beam 53 irradiated from a lid 51 side. As shown in FIG. 28, in the electron beam welding, a sealing material 52, such as a brazing metal material, is disposed between a housing 50 and the lid 51 that is arranged on the upper surface of the housing 50 so as to seal an opening of the housing 50. The electron beam 53 is then sequentially scanned in a predetermined direction from the lid 51 side along the rim of the lid 51 to perform the electron beam irradiation. Here, the electron beam 53 is irradiated so that the starting point and the terminal point of the beam irradiation coincide at a point P. With such irradiation of the electron beam 53, the sealing material 52 is heated and melted, thereby the housing 50 and the lid 51 are welded by the sealing material 52, resulting in a sealed electronic component 54 which houses an electronic component (not shown) being sealed.
Meanwhile, in the foregoing electron beam welding, if gas is generated upon the sealing material 52, e.g., the brazing metal material, being melted and the gas is enclosed within the sealed electronic component 54, it affects the characteristics or reliability of the electronic component (not shown). For example, with the sealed electronic component 54 constituted by housing a quartz oscillator, the gas produced upon welding increases an equivalent series resistance value (CI value) of the quartz oscillator, which in turn decreases the oscillation property of the quartz oscillator. Therefore, in the electron beam welding, it is necessary to discharge the gas produced upon the sealing material 52 being melted, and to prevent the gas from being enclosed within the sealed electronic component 54.
As a method of preventing the gas from being enclosed within the sealed electronic component 54, there is a method, as shown in FIGS. 29 and 30, which irradiates, instead of irradiating over the entire rim of the lid 51 at one time, respective predetermined areas of the circumference of the lid 51 in multiple times with the electron beam 53 (see, for example, Patent Documents 1 through 4). In this method, firstly, as shown in FIG. 29, a predetermined area is set as a non-irradiation area 55 preliminarily, and the electron beam 53 is scanned sequentially for the areas other than this in a predetermined direction along the rim of the lid 51 to perform the beam irradiation. Here, it is set so that the non-irradiation area 55 is formed between the points P and Q, and the electron beam 53 is irradiated from the point P as the starting point to the point Q as the terminal point.
Since the non-irradiation area 55 is not irradiated with the electron beam 53, the sealing material 52 thereon is not melted and the area remains unwelded. Hereinafter, the unwelded area formed in the non-irradiation area 55 is referred to as an unwelded section 55′. This unwelded section 55′ can be used as a gas outlet. After discharging the gas through the unwelded section 55′, the unwelded section 55′ is irradiated with the electron beam 53 so as to weld the section as shown in FIG. 30. In welding the unwelded section 55′, the electron beam 53 is scanned in the same direction as the case of FIG. 29 which welded a section other than this to perform the beam irradiation. Here, the electron beam 53 is irradiated from the point Q as the starting point to the point P as the terminal point. According to the foregoing method, the sealed electronic component 54 can be sealed while preventing the gas from being enclosed within the housing 50.
In addition, since the housing 50 made of a ceramic has such as atmospheric impurities or moisture (hereinafter, these are referred to as a volatile component collectively) on its surface for example, the volatile component needs to be removed. In Patent Document 2, for example, the housing 50, the sealing material 52, and the lid 51 are pre-heated before irradiating the electron beam to remove the volatile component from the respective members.
Moreover, in Patent Document 3, by heating to dry the sealed electronic component 54 with the unwelded section 55′ being formed, gas particles adhered to the housing 50 and the lid 51 are effectively removed.
Patent Document 1: Japanese Patent Laid-open Publication No. 2000-196
Patent Document 2: Japanese Patent Laid-open Publication No. 2000-223604
Patent Document 3: Japanese Patent Laid-open Publication No. 2001-257279
Patent Document 4: Japanese Patent Laid-open Publication No. 2002-141427